1. Field of the Invention
The invention relates to method and apparatus for eliminating errors in a seek operation on a recording medium.
2. Background of the Related Art
In a disk apparatus, such as a disk drive, an optical pickup is moved to a target address on an optical disk loaded therein to read out data from the target address. This is called a seek operation. FIG. 1 shows a flow chart of a related art seek operation.
Specifically, given a target address, the present address of the optical pickup is obtained, in step S0, and the number of tracks to move or jump is calculated, in step S1. In step S1, the number of tracks to move is calculated based on a difference between the present track and the first inner track of a target track containing the target address (hereinafter, referred to as the “pre-target track”). If the number of tracks to move is zero, in step S2, it is determined that the optical pickup has reached the pre-target track. Otherwise, the seek operation continues so that the optical pickup is moved by the re-calculated number of tracks and then address information, such as sub-Q, is read out again at that address on the optical disk, in step S3.
If the target address has not been sought for a predetermined period of time, a seek retry counter, ‘SEEKRetryCnt’ is increased by 1, in step S4. And then, if ‘SEEKRetryCnt’ is smaller than a predetermined seek retry number of times, ‘SEEK_RETRY_LIMIT’, in step S5, steps S0 and S1 are repeated; otherwise, it is determined that a seek error occurs, in step S6. The seek operation error may be caused by a servo-control error or a delay of phase-locking of a phase-locked loop (PLL) circuit by which a clock of a PLL circuit is phase-synchronized to a signal read out from the optical disk. The latter case is described below in detail with reference to FIG. 2.
Given a target address CT, on the track #21 in FIG. 2), the optical pickup is moved to the pre-target track (track #22 in FIG. 2). A laser beam of the optical pickup is positioned on the pre-target track and then reaches near the target address by performing a tracking operation along the spiral track. During the tracking operation, eight-to-fourteen modulation (EFM) signals are read out from those tracks. By phase-locking a clock of the PLL circuit to the EFM signal, sub-Q data can be read out and used to determine whether or not the target address is sought.
Phase synchronization between the clock of the PLL circuit and the EFM signal may fail during the pickup transition from the pre-target track to the target address (T1 in FIG. 2), which is caused mainly by a large phase difference between them. If this occurs, and thus if the phase synchronization is completed on other tracks passing the target address (for example, track #23), the same operations as before are executed once so as to seek the target address by moving the optical pickup to the pre-target track and performing the phase synchronization of the PLL clock.
If phase synchronization between the clock of the PLL circuit and the EFM signal fails again during the pickup transition to the target address, the same seek operations including the optical pickup movement and the PLL clock phase-locking are repeated until the target address is sought. A seek error occurs if the seek operation is not made for a predetermined number of times or a predetermined period of time.